could anyone help me how to fix the numbers when the code runs for more than one iterations

For the following command line

rows=unused_rows(randsample(length(unused_rows),N_UE_rows)),

when i run the code the number of rows keep on changing for more than one iterations as randsample is being used.

But the number of rows need to be fixed when i run for more than one iterations.

could anyone help me how to modify the command line such that the number of rows needs to be fixed for more than one iterations.